This invention relates to electrical inductance coils, and more particularly to a shielded inductance coil capable of being trimmed to predetermined diverse specifications.
The fabrication of electronic circuits, and especially microcircuits, requires the combination of a number of discreet electrical components each of which must meet a specified set of tolerances in order to bring the circuit to within specified limits of design characteristics. This can be achieved in some instances by carefully measuring and evaluating each component to provide matched circuit elements. This procedure is time consuming and costly. In other instances even this procedure is ineffective because of the unpredictability of the effects of leads and contacts on circuit characteristics.
In the use of inductance coils, which depend for their performance on the formation of a magnetic field, it is often necessary to shield them from extraneous magnetic fields and also to shield other circuit components from the stray magnetic fields of the coils, while still affording adjustment of the inductance and inductive reactance of the coils.
The procedure generally employed in adjusting the inductance and inductive reactance of a coil involves the shorting of some of the turns. However, this procedure only provides a coil of a predetermined, fixed inductance and inductive reactance, and can only result in a decrease in the inductance and inductive reactance of the original coil.
Shielding of inductance coils, by enclosing them in containers of magnetic metal, is well known, and is utilized in conjunction with the foregoing adjustment procedure to provide shielded coils having a predetermined, fixed inductance.
However, the provision of a shielded coil capable of variable adjustment, heretofore has been applicable only to standard sizes of radio frequency coils, and has involved complex construction which renders difficult any subsequent readjustment of the inductance.